1. Technical Field
The present invention relates to an exposure device and an image forming apparatus, and more particularly to an exposure device having an optical housing, and an image forming apparatus having the exposure device.
2. Background Art
In the field of image forming technologies using electrophotography, typical image forming apparatuses include an exposure device, a photoconductor drum, and an optical deflector such as a polygon mirror. In such image forming apparatuses, the exposure device scans the photoconductor drum along the axial direction using a laser beam while rotating the photoconductor drum to form a latent image on the photoconductor drum.
With advances in technology, image forming apparatuses having color printing and high-speed printing capabilities have been introduced into the market. In line with such market trends, image forming apparatuses equipped with a plurality of photoconductor drums (typically four) have been introduced. Such tandem-type image forming apparatuses are larger in size due to the increase in the number of photoconductor drums. However, increasingly the market also demands more compact image forming apparatuses, including a concomitant demand for smaller, thinner exposure devices.
For example, JP-S60-32019-A, JP-H07-144434-A, and JP-2010-160295-A disclose configurations to reduce the size and thickness of the exposure device by partially overlapping optical paths of a plurality of laser beams directed from the optical deflector onto each one of the photoconductor drums.
In such image forming apparatuses, when a latent image is formed on a surface of the photoconductor drum, rotation of the optical deflector causes vibrations that result in deformation of the optical housing of the exposure device. Such deformation causes stripes or banding to appear on the output images.
Various methods have been proposed to suppress the vibrations at the exposure device. For example, JP-4299103-B (JP-2005-138442-A) discloses an optical scanner having a housing made of sheet metal that encases optical parts. Attachments are disposed on the bottom face of the housing at at least two places along the long side of the optical parts at positions corresponding to nodes of vibration. An optical part supporting member that supports the optical parts is attached at the attachments to isolate the optical part supporting member from the bottom face of the housing while attached to the nodes of vibration.
Moreover, there is an additional source of vibration. When forming a latent image on the surface of a photoconductor drum, vibrations from mechanical parts disposed in the image forming apparatus are transmitted to the exposure device. By reducing the size of the exposure device, the size of optical elements included in the exposure device also becomes smaller, and thereby the optical elements are more vulnerable to external vibrations. Further, by reducing the thickness of the exposure device, the rigidity and natural frequency of the optical housing are decreased, making the optical housing more likely to resonate with external vibrations. As a result, the vibrations of the optical elements and vibrations of the optical housing are more likely to be superimposed, resulting in marked deterioration of image quality.
The configuration of the optical scanner disclosed in JP-4299103-B (JP-2005-138442-A) can suppress the effects of vibration on the exposure device. However, it is difficult to design the optical housing to locate the nodes at a given position, and also difficult to dispose the optical elements exactly at the nodes.